1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a facsimile apparatus, a printer that can retract a latent image writing unit to a retracted position from an operating position.
2. Description of the Related Art
In typical electrophotographic image forming apparatuses, a configuration in which a latent image is written on a uniformly charged latent image carrier with a latent image writing unit has been widely adopted. The latent image carrier is generally a photosensitive body and the latent image writing unit is generally a laser writing device. In such image forming apparatuses, depending on a layout of the apparatus, maintainability of the latent image carrier and various types of peripheral devices such as a developing device disposed at the periphery of the latent image carrier may degrade because the optical writing unit comes in the way as an obstacle.
In Japanese Patent Application Laid-open No. 2007-164141, an image forming apparatus that includes an optical writing unit is disclosed. The optical writing unit moves between an operating position where a writing operation to write a latent image on a latent image carrier is carried out, and a retracted position where the writing operation is not carried out. With such a configuration, the latent image carrier and the peripheral devices can be exposed outside, by retracting the optical writing unit to the retracted position from the operating position opposed to the latent image carrier. Accordingly, the maintainability thereof can be improved.
FIG. 11 is a perspective view of an internal configuration of an image forming apparatus disclosed in the Japanese Patent Application Laid-open No. 2007-164141. As shown in FIG. 11, the image forming apparatus includes a holding frame 230 that is a holder for holding a casing 271 of an optical writing unit 270 that includes a polygon motor, a polygon mirror, and a reflecting mirror, which are not shown.
A first holding plate 232 of the holding frame 230 includes a first opening 232a and a second opening 232b arranged with a predetermined distance therebetween. A left side first alignment axis 271a protruding from a left side surface of the casing 271 is inserted through the first opening 232a, while allowing a certain degree of freedom therein. On the other hand, a left side second alignment axis 271b protruding from the left side surface of the casing 271 is inserted through the second opening 232b, while allowing a certain degree of freedom therein.
A second holding plate 233 of the holding frame 230 includes a first opening 233a and a second opening 233b arranged with a predetermined distance therebetween. A right side first alignment axis 271c protruding from a right side surface of the casing 271 is inserted through the first opening 233a, while allowing a certain degree of freedom therein. On the other hand, a right side second alignment axis 271d protruding from the right side surface of the casing 271 is inserted through the second opening 233b, while allowing a certain degree of freedom therein.
The first holding plate 232 and the second holding plate 233 are rotatably supported by a rotation axis 200 laid across a first support plate 280 and a second support plate 290 of the apparatus main body. By rotating the holding frame 230 around the rotation axis 200, it is possible to retract the optical writing unit 270 to a retracted position from an operating position.
A left side first optical alignment groove 281a and a left side second optical alignment groove 281b recessed by a predetermined depth are arranged with a predetermined distance therebetween, at an upper end of the first support plate 280. On the other hand, a right side first optical alignment groove 291a and a right side second optical alignment groove 291b recessed by a predetermined depth are arranged with a predetermined distance therebetween, at an upper end of the second support plate 290.
When the optical writing unit 270 is at the operating position, the optical writing unit 270 is supported by bringing each of the alignment axes 271a to 271d of the casing 271 pressed against the bottom surfaces of the corresponding optical alignment grooves 281a, 281b, 291a, and 291b, respectively. Accordingly, the optical writing unit 270 is aligned in a vertical direction.
In the Japanese Patent Application Laid-open No. 2007-164141, as shown in FIG. 12, an image forming apparatus in which the optical writing unit 270 is supported at three points at the operating position is also disclosed. More specifically, the alignment axes 271a and 271c are protruded from the left side surface and the right side surface of the casing 271, respectively. The alignment axes 271a and 271c are supported by bottom surfaces of the optical alignment grooves 281 and 291 provided at the top end of the first support plate 280 and the second support plate 290, respectively. A rotation axis engaging unit 271e, provided at the center in a left-right direction of the rear side plate of the casing, is engaged to the rotation axis 200, and the rotation axis 200 supports the casing 271 of the optical writing unit 270.
When the optical writing unit 270 is supported at four points as shown in FIG. 11, it is necessary to perform accurate alignment of the four support units. This may result in an increase in manufacturing cost and the like. When the optical writing unit 270 is supported at three points, as shown in FIG. 12, it is only necessary to perform accurate alignment at three points. Accordingly, it is possible to reduce manufacturing cost, compared with the optical writing unit supported at four points.
However, in the image forming apparatus shown in FIG. 12, one point among the three support points is supported by the rotation axis 200. Because the rotation axis 200 is less stiff compared with the side plate, when a disturbance, such as a user bumping into the apparatus main body occurs, the rotation axis 200 vibrates, and the vibration are disadvantageously transmitted to the casing 271. Consequently, the reflecting mirror and the like in the casing vibrate. If the reflecting mirror and the like vibrate, the reflection direction of light fluctuates, thereby shifting the irradiating position. As a result, problems such as color shifts occur.